Aright, I ordered a set of new 12ax7's from Dougstube's and replaced my old ones. Everything went smoothly for about a week. Now, there's an incredibly loud humming noise whenever the amp is on. I opened the back up where the 12ax7's are, replaced all of the new ones with the old ones, and tried again. Same problem. Also, no matter how I arrange the tubes in the back, it seems like there's always at least one or two tubes that don't light up as the others do. What does this problem sound like to you guys?

Head with an Uber Cab. I replaced the tubes because I bought the head used over a year ago, and the head was starting to produce noticeably more white noise as time went by. Nothing like the noise it's making now, though.

For pulling the power tubes if you plug your cab into half the impedance (16ohm cab into 8ohm, 8ohm into 4) then you can safely leave it on without it having to be a quick check.

If pulling the power tubes doesn't help, try pulling the preamp tubes one by one, starting nearest the input jack. My hunch is failing filter caps on the preamp tube rectifier circuit (you don't need to know what that means, but if the noise goes away when V1-4 are out its a distinct possibility and you can at least ask your tech to check).